SINGLE CRYSTAL STRUCTURE DETERMINATION AT PRESSURES EXCEEDING 20 GPA WITH SYNCHROTRON RADIATION. Stefan Werner, Julie Kim-Zajonz, Jürgen Wittlinger, Heinz Schulz, Institut für Kristallographie und Mineralogie, Ludwig-Maximilians-Universität München, Theresienstr. 41, D-80333 München, Germany

Employing a newly developed diamond anvil cell a pressure of 31 GPa was achieved in an angle dispersive single crystal X-ray scattering experiment on ruby and a pressure of 21 GPa in an experiment on the amorphisation of ZnCr₂S₄-spinell.

The principles of this cell design are presented. The cell is loaded with the single crystal specimen, a small ruby crystal as pressure calibrant and cryogenic argon as (quasi)hydrostatic pressure transmitting medium.

Scattering experiments were performed at beamlines D3 and F1 at HASYLAB / DESY.

The centering of the cell on the diffractometer is controlled by the profile of the primary beam which has passed the pressure cell.

A pneumatically driven collimator on the secondary beam was developed to exclude X-rays scattered by the beryllium backing plate facing the detector.

Systematic falsifications of intensity data caused by scattering of the diamond single crystals are calculated in advance and are detected by measuring reflection intensities at different y-angles.